1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same. More particularly, the invention relates to a semiconductor device having a capacitor using a dielectric and to a method of manufacturing this semiconductor device.
2. Description of the Related Art
Ferroelectric random access memories (FeRAMs) are nonvolatile memories that have a ferroelectric thin film. They differ from DRAMs in that a ferroelectric is used in place of the capacitor section of the DRAM. They are expected to be the next-generation memories.
The FeRAM has a capacitor section that is a ferroelectric thin film made of PZT (Pb(ZrxTi1-x)O3), BIT (Bi4Ti3O12), SBT (SrBi2Ta2O9), or the like. These materials are of perovskite structure, the basic element of which is oxygen octahedron. Unlike Si oxide film that has been conventionally used, they do not exhibit ferroelectric property that characterizes them, so long as they remain amorphous. Hence, they cannot be used in amorphous state. To be used, they need to be crystallized by means of, for example, high-temperature heat treatment or high-temperature in-situ process. Generally, they must be processed at a temperature of at least 400 to 700° C. Note that the temperature depends on the material. MOCVD process, sputtering process, and chemical solution deposition (CSD) are available as methods of forming a film of any one of these materials.
The FeRAM capacitor having a member of such a ferroelectric material as described above exhibits good characteristics after the capacitor film has been formed. When a RIE process, an inter-layer film forming process, a wiring process, a sintering process, or a molding process is carried out thereafter, the capacitor may be damaged by diffusion of H or the like to have its characteristics degraded.
To lessen the damage to the capacitor during any process that follows the process of forming the capacitor film, a protective film is used. Jpn. Pat. Appln. KOKAI Publication No. 2001-36026 discloses a capacitor cell. The capacitor cell has an Al oxide film, which is a protective film provided on the top of the capacitor. The capacitor cell is therefore protected from damages. The Al oxide film may be formed by sputtering process, CVD process or the like. Jpn. Pat. Appln. KOKAI Publication No. 2002-43541 discloses an atomic layer deposition (ALD) method that realizes high step coverage in the micro-fabrication that achieves high integration density.
To enable the FeRAM to operate reliably, the circuits peripheral to the FeRAM have capacitors designed to stabilize the power. PZT capacitors are used, on trial basis, in the circuits peripheral to the FeRAM in order to stabilize the power. This is because PZT has high permittivity. Jpn. Pat. Appln. KOKAI Publication No. 2002-343942, for example, discloses a technique of forming ferroelectric capacitors in the memory-cell array region and forming, at the same time, dummy capacitors in the peripheral-circuit region. Further, U.S. Pat. No. 6,404,001 discloses a technique of forming ferroelectric capacitors for the memory cells, at the same time as the capacitors for the peripheral circuits. However, PZT capacitors have a large leakage current. This makes it difficult to reduce the thickness of the PZT capacitors for increasing the capacitance.